Changing times call for changing America's role in the world.

Cal Thomas is a conservative columnist. Bob Beckel is a liberal Democratic strategist. But as longtime friends, they can often find common ground on issues that lawmakers in Washington cannot.

BOB: Despite lukewarm, or in some cases scathing, reviews of President Obama's speech at West Point's graduation last week, he raised the most important question we as a nation must address: When should we use U.S. military power abroad, and should we send troops only when our national security interests are affected?

CAL: The president is right that we can't solve the problems of the world or protect our national security with military power alone. We are transitioning from an old model of front lines and nation states to one that primarily involves terrorists operating within and across borders, and cyberwarfare that includes Chinese computer hackers. We need a national debate on this, Bob. Right now, the public appears tired of foreign adventures, but we can't afford to give up. Our enemies aren't quitting.

BOB: I agree, and it is a discussion well past due. I'm reading a book on World War II where U.S. national interests became clearer and clearer as the Nazis and Japanese moved to dominate most of the world, despite strong isolationist feelings in the U.S. The great land, sea and air battles of that war will never be repeated, and yet we still have a military structure that hasn't radically changed since that war.

CAL: I'm reading a book about World War I, whose centenary will be observed in August. In that book by Max Hastings, called Catastrophe 1914, some European nations used 19th century battle tactics, while Germany employed modern weapons and strategies. We need a comprehensive strategy that includes not only drones and weapons, but also better monitoring of those who could cause us harm. For example, I'm thinking of those Americans who went to Syria and other countries to fight for jihadists. They should have their citizenship revoked.

BOB: I agree, and the sooner the better. U.S. military forces and facilities are not just in Afghanistan and Iraq but also Germany, Japan, South Korea and Italy, to name a few. Many of these troops were committed in treaties over half a century old. It's time to review those obligations, given the staggering cost to our budget.

CAL: President Kennedy's line about America's willingness to "pay any price, bear any burden" to ensure the success and survival of liberty was fine for the Cold War, but we can no longer afford it. Obama's request for $1 billion to increase America's military presence in Europe is probably aimed at Russia's Vladimir Putin in light of his adventurism in Crimea and pressure in Ukraine. I'm OK with that as long as our allies help pay most of the bill.

BOB: You're right. The cost of the Iraq and Afghanistan wars is well over $1 trillion. The war on terror requires us to commit forces and material in places from Somalia to the Philippines. U.S. taxpayers are mostly paying the bill. How much longer are we going to ignore crucial needs within our borders?

CAL: No one knows how many terrorists have managed to slip into this country. Iran claims to have agents here and boasts that in the event of a U.S. attack on its nuclear facilities, those agents will retaliate. Given our porous southern border, I don't believe they are bluffing.

BOB: I favor a comprehensive immigration law that will allow those here illegally to go to the back of the line, but eventually find a path toward citizenship. After that time, we need to shut our borders completely and include the U.S. military to help to keep our borders secure.

CAL: You and I remember a time when the one thing Republicans and Democrats found common ground on was foreign policy. Most politicians once believed criticizing a president's policies abroad conveyed weakness to our enemies. The U.S. won the Cold War, in part, because we were mostly united in our opposition to the spread of communism. Since the Vietnam War, foreign policy has become another political football, and our enemies see opportunities in our division. That's why a national debate about America's role in the world could serve to unite us again, at least on this one issue.

BOB: We can only assume that Islamic terrorists will continue attacking the U.S. at home and abroad. We have been fighting the terrorists largely with American soldiers. President Obama has been criticized for announcing a deadline for the withdrawal from Afghanistan, but he's right. It's time for Afghanistan and Iraq to the stand on their own. We have made use of drones, special forces and international policing and cooperation. There's no reason why terrorism cannot be fought with our high-tech advantages. Special forces and international police work have stopped many terrorist attacks without the involvement of U.S. soldiers.

CAL: What concerns me most about the president's declaration that the war in Iraq is over and the one in Afghanistan is ending is that this is not the view of the Islamic jihadists. Wars are won when one side is defeated. We can't afford to surrender to terrorists, so we had better start discussing how best to defeat them. Another Kennedy line from his 1961 inaugural address speaks to our need of unity: "United there is little we cannot do in a host of cooperative ventures. Divided there is little we can do — for we dare not meet a powerful challenge at odds and split asunder."